Modify Boid collision distance with hard boundary - v2.80
I will go ahead and post this as it works well enough for my use case, though it feels like there's a better solution:

I was able to get the simulation to work if I drastically increased the scale of the whole model - so that even if what earlier felt like a large collision distance remained the same, it would still be relatively small compared to the path the rats would travel through.

If somebody has a better solution I would gladly accept it in place of this one! I would prefer to keep the units life-size as they were before.

Current below: it appears that the relative collision distance from the stairs is the same compared to the images above. On the right of the image, there are still some bouncy rats but I can perhaps add a forcefield to direct them so I'm not too worried about that.